Science of seawater

Thank you for your letter of August 31, 2009. I do appreciate the time that you have taken to answer my email in so much detail.

The comments of Mr Allan Holmes that I was referring to were his statements that “the Science” indicated that to allow seawater into the Lower Lakes would cause damage and you have repeated this in your letter: that introduction of seawater may exacerbate acidification.

There are several aspects of this situation that need clarification.

There are far too many people who make bald statements about what “science” says, but they seldom explain what they mean, or make any reference to the particular work that supports their stance. True science is often not that clear, and sometimes there is disagreement between scientists. As well, some scientists themselves make statements that are beyond the area of their expertise, or are coloured by their own beliefs, which makes it very difficult for an ordinary person, even politicians, to make the right judgements.

Without knowing which “science” Mr Holmes was referring to, I assume that it is linked to the extra sulphate ions that would be introduced with seawater. What is not stated is just how miniscule this would be in comparison to the vast stores of sulphidic materials that already exist in the sediments of the Lower Lakes, and which are being progressively oxidized to sulphuric acid as they are exposed. In fact, much of the areas already exposed contain sulphides which are more concentrated as the result of the permanent and artificially high fresh water level after the barrages were installed (Fitzpatrick and Shand, 2008). The sulphidic sediments are not a problem until they are exposed, and so a tidal estuary solution to the Lower Lakes would keep the sediments covered by the fluctuating fresh and seawater environment.

Even if it could be shown that introduction of seawater to the Lakes caused a small amount of extra sulphides to be formed, this “damage” is far outweighed by the system collapse which could occur if the water levels fall below the suggested trigger point of -1.5m, AHD, where the remaining water body could itself become so acidic and full of toxic metals in solution that virtually none of the existing organisms in the water body would survive. The government’s “last resort” of allowing minimal quantities of seawater in to buffer the Lakes water in this event may turn out to be too little too late. Unfortunately we do not know exactly what this trigger point is, or how much seawater would be necessary, but it is clear that it could become perilously close to an almost irreversible state, given the predictions of a dry spring and summer, and the levels in Lake Alexandrina already at -0.76m AHD.

Allowing the levels to get this low also ignores the importance of the Ramsar treaty, since the former wetlands would be further destroyed. An international expert recently in Adelaide stated that the Ramsar convention accepts the value of marine and estuarine wetlands as equal to freshwater ones. Estuarine wetlands around the Lower Lakes would support a diverse biota which could be seen as more healthy than the situation since the barrages, given that there would be some tidal fluctuations, allowing wading birds to thrive.

You have mentioned the problem of the degree of tidal mixing which could be achieved by opening the barrage gates to the sea. I do not agree “that estuarine conditions could only be maintained for any length of time except in the near proximity of the mouth itself”. This does not take into consideration many factors by which seawater could be moved into and out of the Lakes to prevent hypersalinity. Some of these are:

The flood tide sand accretions behind the mouth which have built up as the result of the barrages would have to be cleared, or at least channels dredged through them to allow the maximum tidal signals to reach the barrages. Dredging is a necessary procedure at the mouths of most tidal estuaries around Australia, but new technologies of resuspension of ebb tide sand would make this job much cheaper and easier. The gates of the barrages would have to be modified so that they could be operated quickly to take advantage of spring high and low tides, storm surges, and seiching patterns in the Lakes. It has been shown that longer period weather patterns have an additional influence on the water levels of the Gippsland Lakes which are much stronger than the tidal influence (Gippsland Coastal Board). These would be expected to occur in SA’s Lower Lakes as well.

Having five barrages to manipulate would allow the use of one or more for entry and others as exit for seawater, depending on the water levels in Lake Alexandrina, thereby allowing circulation within the Lakes. If a channel were cut from Lake Albert through to the Coorong, this could be an additional part of the system of circulation.

All of these mechanisms and others need to be modeled by qualified engineers, of which we abound in South Australia. The trouble with the Government of South Australia’s “fresh water only” stance is that valuable time has passed during which these mechanisms could have been researched. By now we could have had some strategies which could be put into action at short notice if the water levels become critical.

I dispute that the Langhorne Creek vineyards are not at risk of wind blown toxic dust. You only have to look at the Google Earth images to see how these extend right down to the former shores of Lake Alexandrina. The monitoring of wind blown dust by the EPA will be useless when it occurs if nothing has been done to stop it. The so-called “bioremediation” has not been done around the majority of the Lake perimeter, and even if it had been, would probably not work in the longer term, given the highly saline and sulphidic soils which will be further exposed as the water levels drop, and on which plants would not establish and survive. Those advocating treating the so-called “hot spots” have no appreciation of the vast extent of the sulphidic soils, and that these hot spots are merely areas where the acidification reactions have reached their end points, while the remaining areas are still proceeding along the pathways to acidification, and will reach it in time if the drying continues.

It appears to me that the Government of SA perceives that the very vocal Fresh Water Embassy represents the majority of the voting public, and therefore it dare not consider another alternative. I believe that there are a growing number of thinking persons who are now becoming more aware of the true dangers that we face with the continuing unavailability of fresh water from upstream as the result of the drought and mismanagement of the resource, and now see the estuarine alternative for the Lower Lakes as a viable option.

I am not advocating a lessening of the responsibility of the Federal and Sate Governments to reverse the overuse of water upstream through buybacks and restructuring of inefficiencies. However, it seems that these processes are far too slow to have any effect on our present predicament.

Once again, I draw your attention to the website: www.lakesneedwater.org which contains a huge amount of material relevant to the seawater option for the Lower Lakes.